The present invention relates to a prosthesis, in particular a foot prosthesis, for the fitting of leg amputees, according to the preamble of patent claim 1.
The biomechanical processes of human walking are composed of a plurality of movements of individual body parts. In the course thereof extremely complex processes are taking place in the region of the lower extremities. Here various joints cooperate synchronously and synergistically in order to cushion the reaction forces occurring at the point of origin, which means the treading plantar-Surface of the foot, in order to conduct propelling forces efficiently into the ground and to compensate potential unevennesses on the ground such that the rest of the body does not need to perform energy consuming compensatory movements. The joints in the foot assume therein great significance in particular the upper ankle joint (OSG) and the lower ankle joint (USG). Each of the two ankle joints located in the proximity of the malleolus of a human foot has a rotational axis with a specific orientation with respect to the other. FIG. 12a to 12h show the progression of the rotational axis A of the upper ankle joint and of the rotational axis B of the lower ankle joint relative to the human foot. For simplification of the explanation, here a spatial system of coordinates with the axes X, Y and Z is introduced, where the X-Y plane is defined by the fixed points 10, 12 and 14 of the human foot and the direction of the X-axis by its longitudinal extent, wherein further the Y-axis is always directed toward the outside of the foot and the Z-axis is orthogonal to axis X, and Y extends substantially in the longitudinal direction of the lower leg in the relaxed resting position of the foot 16.
If such a system of coordinates is assumed, it can be seen that the rotational axis A of the upper ankle joint is inclined in the X-Z plane according to FIG. 12c substantially at 10° relative to the X-axis, in the X-Y plane according to FIG. 12c substantially at 82° relative to the Z-axis and in the X-Y plane according to FIG. 12e substantially at 6° with respect to the Y-axis. It can further be seen that the rotational axis B of the lower ankle joint is inclined in the X-Z plane according to FIG. 12f substantially at 41° with respect to a line parallel to the X-axis, in the Y-Z plane according to FIG. 12g substantially at 45° with respect to the Y-axis and in the X-Y plane according to FIG. 12h substantially at 23° with respect to the X-axis. These progressions of the rotational axes of the upper ankle joint OSG and of the lower ankle joint USG in a normal gait pattern of a healthy human foot lead to specific movement sequences, in particular to relative movements between lower leg and foot. For an explanation of these movement sequences reference is made to FIG. 13a and 13b. FIG. 13a shows the movements when the foot 16 is placed on a ground U up to the middle stance phase. FIG. 13b shows the further movement sequence when the foot 16 is rolled over the ball of the foot.
When placing the foot according to FIG. 13a an inner rotation of the lower leg according to arrow 18 occurs due to a rotation of the hip and to a simultaneous eversion (outward rotation) of the foot according to arrow 20, until the middle stance phase according to FIG. 13a has been reached. In the succeeding roll-off and push-off according to FIG. 13b, in contrast, an outer rotation of the lower leg occurs according to arrow 22 and, on the other hand, an inversion of the foot takes place synchronously, according to arrow 24. These cooperating movements according to FIG. 13a and 13b in the proximity of the upper and lower ankle joint of the human foot are decisive for the efficient cushioning of ground reaction forces and a restrained transfer of the rotation of the human hip to the ground, and conversely, during human walking, such that the movement apparatus can be utilized efficiently and with restraint.
The challenge has existed for a long time in the field of prosthetics to simulate the complicated biomechanical processes in the lower extremities as exactly as possible in a prosthetic device in order to be able offer patients whose legs had been amputated prosthetic devices which permit mimicking the complex human gait as authentically as possible. For this purpose it is necessary to provide the individual prosthetic devices with joints, which, on the one hand, ensure sufficient stabilization for the legless person, however, on the other hand, have such flexibility that they make possible the unimpeded locomotion of a person. An essential aspect is herein that the gait pattern achieved is as economic as possible, in order to keep the efforts in the forward progression of the legless person low. It must be taken into consideration that leg amputees are often patients with at least a restricted degree of mobility, whose training status is weakly developed so that additional efforts caused by the dynamic behavior of the prosthetic device could further restrict the degree of mobility. It must moreover be taken into consideration that with a nonsymmetric gait pattern, due to the dynamic behavior of the prosthetic device, damage to the vertebral spine, in particular the lumbar portion of the spine, may occur. A nonsymmetric gait pattern due to a prosthesis can moreover lead to unusually strong stress or even to wear phenomena on the healthy leg as well as on the still functioning knee joint ligament of the amputated leg. In addition to the disablement due to the amputation, hip damage, damage to the inter-vertebral disks, joint instabilities or even arthrosis may develop as a consequence of such unnatural stresses.
Attempts have therefore been undertaken in prior art to provide through various measures prosthetic devices which at least approximately exhibit similar dynamic behavior as a natural human foot during normal human walking.
U.S. Pat. No. 5,425,780 discloses a lower leg prosthesis of the above described type, in which via a universal [Cardan] joint a foot section is connected with a lower leg shaft. The device shown here is structured in such a way that it is relatively complicated and requires much space, which is of disadvantage in particular in view of its weight and wearing comfort. Moreover, this prior art prosthesis exhibits dynamic behavior which strongly differs from the natural dynamic behavior of a human foot, since the orientation of the universal [Cardan] axes deviate significantly from the orientation of the biomechanical axes of the upper and the lower ankle joint.
WO 94/22399 describes a foot prosthesis which is also provided with a universal joint. The universal joint in this foot prosthesis is formed by a pivot pin as well as a pivot bearing rotationally receiving the bearing pin orthogonal to its longitudinal extent. While thereby a movement of the foot prosthesis about two axes relative to the shaft can be realized, however, the axes, again, are oriented significantly discrepant from the biomechanical axes of the upper and lower ankle joint. The axis position, moreover, also deviates markedly from the axis position of the upper and lower ankle joint. The two rotational axes are not located in a region proximal to the treading attachment, but rather markedly above the treading attachment, that means at a site at which no rotational movement takes place in a natural human foot. This foot prosthesis also leads to an unnatural gait pattern and to the above described disadvantages for the patient with respect to excessive loading. The same disadvantages are entailed in the foot prostheses known from documents AT 16 22 41, U.S. Pat. No. 2,692,990, U.S. Pat. No. 2,644,165 and DE 804 830.
As further prior art is cited U.S. Pat. No. 5,314,499. This prior art provides a foot prosthesis with a single pivot joint to connect the shaft with the treading attachment. The above described corresponding relative rotational movements during the process of natural walking cannot be mimicked with Such a one-axis joint.
For technical background of the present invention reference is further made to prior art according to EP 1 128 789 B1, U.S. Pat. No. 5,800,570, U.S. Pat. No. 4,892,554 and EP 0 498 586.
Further, a foot prosthesis is disclosed in DE 42 08 941 C2, which, in the interest of a mechanically simple structure, attempts to suffice entirely without joint element.
From the category-defining prior art according to DE 818 677 a foot prosthesis is known in which a universal joint mechanism couples a treading body with a shaft. The disposition and the orientation of the universal joint mechanism in this arrangement also differs significantly from the biomechanical axes of the upper and the lower ankle joint, such that the foot prosthesis leads to all unnatural gait pattern and to the above multiply addressed unnatural loading for the patients. There is furthermore a damping element provided, which is disposed about the universal joint mechanism and cooperates with the shaft in order to dampen a relative movement of the shaft relative to the treading body. This disposition of the damping element ensures, for one, a biomechanically unnatural damping behavior of the foot prosthesis and, for another, moreover leads to a structural form requiring relatively large space.
The problem addressed by the present invention, in contrast, is to provide a prosthesis of the above described type in which a compact structure is capable of modeling the biomechanical processes of the natural, i.e. physiological, gait pattern of man in the region of an upper and lower ankle joint and to do so as authentically as is possible.
This problem is solved according to the invention through a prosthesis—in the following also referred to as “prosthetic device”—with the characteristics of patent claim 1.